CN103050133B - Glass base plate for magnetic recording carrier and employ the magnetic recording media of this glass base plate for magnetic recording carrier - Google Patents

Abstract

The object of the present invention is to provide a glass substrate for magnetic recording media and a magnetic recording medium using the glass substrate for magnetic recording media, wherein at least one main plane (recording and reproducing surface) of the glass substrate for magnetic recording media When the surface roughness Ra was measured for each set evaluation area in a grid shape, the maximum value was within a predetermined range. Provided are a glass substrate for a magnetic recording medium and a magnetic recording medium using the glass substrate for a magnetic recording medium. The glass substrate for a magnetic recording medium has a pair of main planes, and is characterized in that on at least one of the main planes The maximum value of the surface roughness Ra measured in the grid-shaped evaluation regions set on the entire plane surface is 1.7 times or less the average value of the surface roughness Ra.

Description

Glass substrate for magnetic recording medium, and glass substrate for magnetic recording medium using the same magnetic recording media

technical field

The present invention relates to a glass substrate for a magnetic recording medium, and a magnetic recording medium using the glass substrate for a magnetic recording medium.

Background technique

Conventionally, aluminum alloy substrates have been used as substrates for magnetic recording media used in magnetic disk recording devices and the like. However, in recent years, glass substrates that are harder than aluminum alloy substrates and have excellent flatness and smoothness have become mainstream in response to demands for high-density recording.

In addition, with the increase in recording density of magnetic disks (hereinafter, also referred to as magnetic recording media) in recent years, magnetic signals are recorded finely on the magnetic disks, and the signals become weaker as a result. In order to read and record such weak signals, it is required to shorten the distance between the magnetic disk and the magnetic head as much as possible.

In order to reduce the distance between the magnetic disk rotating at high speed and the magnetic head, that is, the floating amount of the magnetic head, it is necessary to make the surface of the magnetic recording medium glass substrate, which is the substrate of the magnetic disk, extremely uniform so that the magnetic disk does not come into contact with the magnetic head.

In order to reduce the distance between the magnetic head and the magnetic disk, various studies have been made on the surface properties of the glass substrate for magnetic recording media. For example, Patent Document 1 describes that the shape of a defect existing in a glass substrate for a magnetic disk influences the surface roughness Ra to be a predetermined value or less.

【Prior technical literature】

【Patent Literature】

[Patent Document 1] International Publication No. 2010/001843

However, in Patent Document 1, the surface roughness Ra is only evaluated for a limited part of the recording and reproducing region of the glass substrate for magnetic recording media by an atomic force microscope, and the surface roughness Ra is not evaluated for most of the recording and reproducing region. Since the surface roughness Ra is measured, there may be an area where the value of the surface roughness Ra increases in the recording/reproducing area, which may cause a problem. For example, there are problems that it is difficult to reduce the floating amount of the magnetic head, and the distance between the magnetic disk and the magnetic head is unstable, and magnetic noise is generated.

In addition, when manufacturing a magnetic recording medium, a magnetic layer is formed on the surface of a glass substrate for a magnetic recording medium, but there is a region where the value of the surface roughness Ra is high on the main plane of the glass substrate for a magnetic recording medium (the surface roughness Ra non-uniform region), the size of the crystal grains of the formed magnetic layer may be non-uniform. A magnetic recording medium having a non-uniform magnetic layer (a magnetic layer with non-uniform crystal grain size) may generate increased magnetic noise in regions where the crystal grain size is non-uniform, based on the read and write of the magnetic head to the magnetic recording medium There are problems such as a decrease in accuracy and a decrease in recording density.

Contents of the invention

In view of the problems in the prior art described above, an object of the present invention is to provide a glass substrate for magnetic recording media in which the surface roughness Ra is within a predetermined range on the entire surface of at least one main plane (recording and reproducing area) of a glass substrate for magnetic recording media. Glass substrate for magnetic recording media.

In order to solve the above-mentioned problems, the present invention provides a glass substrate for magnetic recording media, which has a pair of main planes, and is characterized in that, on at least one of the main planes, each evaluation area in a grid shape set on the entire surface of the main planes The maximum value of the measured surface roughness Ra is 1.7 times or less the average value of the surface roughness Ra.

【Invention effect】

The glass substrate for a magnetic recording medium of the present invention (hereinafter, sometimes simply referred to as a "glass substrate") was measured in each evaluation area in a grid pattern set on the entire surface of at least one main plane of the glass substrate ( Arithmetic mean roughness) Ra, its maximum value and average value are in a prescribed relationship.

Therefore, on the entire surface of at least one main plane of the glass substrate, the surface roughness Ra is within a predetermined range, and there is no region where the surface roughness Ra is locally high, so that the entire surface of the main plane is uniform and smooth.

According to the glass substrate for a magnetic recording medium of the present invention, it is possible to provide a magnetic recording medium that suppresses coarsening of crystal grains when forming a magnetic layer on the surface of the glass substrate and has a smooth surface of the magnetic layer with uniform crystal grain sizes.

Thus, the occurrence of magnetic noise of the magnetic recording medium can be suppressed, the distance between the magnetic recording medium and the magnetic head can be reduced compared to the past, the distance between the magnetic recording medium and the magnetic head can be stabilized, and the recording accuracy of the magnetic recording medium can be improved. Read and write accuracy and recording density are higher than ever.

Description of drawings

FIG. 1 is an explanatory view of a glass substrate for a magnetic recording medium and an evaluation region thereof according to a first embodiment of the present invention.

detailed description

Hereinafter, modes for implementing the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments, and various modifications and substitutions can be added to the following embodiments without departing from the scope of the present invention.

[first embodiment]

In this embodiment, the glass substrate for magnetic recording media of this invention is demonstrated.

The glass substrate for magnetic recording media of the present invention is characterized in that, on at least one main plane of the glass substrate for magnetic recording media, the surface roughness Ra measured in the grid-shaped evaluation regions set on the entire main plane is The maximum value of is less than or equal to 1.7 times the average value of the surface roughness Ra.

A specific evaluation method will be described using FIG. 1 .

As shown in FIG. 1(A) , the glass substrate for a magnetic recording medium has a disc shape having a circular hole in the center. Furthermore, in the present invention, the surface roughness Ra is measured in each grid-shaped evaluation area set on at least one main plane of the glass substrate, that is, the entire recording and reading area in the case of a magnetic recording medium. As shown in FIGS. 1(A) and (B), the evaluation area is formed by dividing the main plane into a plurality of parts without gaps. It is preferable to form the evaluation regions into the same shape.

The method of measuring the surface roughness (arithmetic mean roughness) Ra is not particularly limited, as long as the surface roughness can be measured in each evaluation area set in a grid pattern over the entire surface. For example, it can be measured with a scanning interference microscope or the like.

The shape and size of the evaluation area set in a grid shape are not particularly limited. For example, the shape of the evaluation area includes square grids, triangular grids, hexagonal grids, rhombus grids, rectangular grids, and parallel grids. .

As the size of one evaluation area, for example, when the shape of the evaluation area is a square grid, the length of one side can be set within the range of 5 μm to 50 μm, such as 50 μm square, 40 μm square, 30 μm square, or 20 μm Square etc. desired size.

In addition, when the shape of the evaluation region is other than a square grid, it is possible to set a size based on this, that is, so that the area of the evaluation region becomes the same area range as that of the square grid (for example, 25 μm ² ~2500 μm ² ) to set this dimension. It should be noted that in the following, the size of the evaluation area is based on the length of one side of the square grid, but it is not limited to the square grid. In the case of other than the square grid, this is the standard size (area).

In addition, the shape and size of the evaluation area set in a grid pattern may be different on the entire surface of the main plane (for example, the entire surface of the main plane is divided into predetermined areas, and the shape and size of the evaluation area are set in each area. etc.), preferably the same.

In particular, it is preferable to perform evaluation in each region having the same size as the magnetic head or a smaller size. Therefore, the size of the evaluation region is preferably 50 μm square or less, more preferably 30 μm square or less.

However, when the size of the evaluation area is too small, the number of evaluation areas increases, the amount of data increases and its handling becomes difficult, so it is preferably 5 μm square or larger, and more preferably 10 μm square or larger.

Here, the evaluation area will be described. 1(A) and (B) schematically show each evaluation area. In addition, although a line is shown in a drawing, this is a line for explaining an evaluation area, and a line is not drawn on a glass substrate actually. Here, the evaluation area will be described using an example of a square grid.

FIG. 1(B) is an enlarged part of FIG. 1(A) for explaining the evaluation region. Each block (for example, the parts shown in (a) to (d)) of the square grid (square) shown in FIG.

Moreover, in the glass substrate for magnetic recording media of this invention, the average value of the surface roughness Ra calculated from the result of the surface roughness measurement about each evaluation area of the whole main plane is Ra _ave . In addition, when the maximum value of the surface roughness Ra, that is, the surface roughness Ra of the evaluation region having the highest surface roughness value in the evaluation region of the entire main plane is Ra _max , Ra _max ≤ 1.7·Ra _ave In other words, the maximum value of the surface roughness Ra is 1.7 times or less than the average value of the surface roughness Ra.

Here, the relationship between Ra _ave and Ra _max is more preferably Ra _max ≤ 1.4·Ra _ave , and particularly preferably Ra _max ≤ 1.3·Ra _ave .

This is because as the ratio of the maximum value of the surface roughness Ra to the average value approaches 1.0, the fluctuation of the surface roughness Ra decreases over the entire surface of the main plane, indicating that the main plane of the glass substrate is smoother (that is, Ra _max ≥ 1.0 _Rave ).

It should be noted that there are two main planes above and below the glass substrate for magnetic recording media. However, when the magnetic disk is used as a recording and reproduction area, either one may be used. In this case, only one of them may satisfy the above requirements. In the case of a magnetic disk, when both the upper and lower surfaces serve as recording/reproducing areas, it is preferable that the average value and the maximum value of the surface roughness Ra measured and calculated for each surface of the upper and lower surfaces satisfy the above requirements. The same applies to average values and standard deviations described later.

In addition, the standard deviation of the surface roughness Ra measured in the grid-like evaluation regions set on the entire surface of the main plane is preferably 0.012 nm or less, more preferably 0.010 nm or less, particularly preferably 0.008 nm or less .

This is because, by reducing the standard deviation, the fluctuation of the surface roughness Ra is small with respect to the entire surface of the main plane of the glass substrate, which means that the main plane of the glass substrate is smoother.

In this way, the entire surface of the main plane is smooth and there is no region with locally high surface roughness Ra. Therefore, when forming a magnetic layer as a magnetic recording medium, local coarsening of crystal grains is suppressed, and the size of the crystal grains is uniform, thereby obtaining Magnetic film with smooth surface.

Therefore, the distance between the magnetic disk (magnetic recording medium) and the magnetic head can be shortened. In addition, since the distance between the magnetic disk and the magnetic head is stable, the generation of magnetic noise can be suppressed, and the read/write accuracy and recording density of recording can be improved compared to conventional ones. In addition, with a magnetic recording medium having a uniform magnetic layer with a small crystal grain size, it is possible to reduce the size of the memory spot and improve the areal recording density of the magnetic recording medium.

In addition, the average value of the surface roughness Ra measured in the grid-like evaluation regions set on the entire surface of the main plane is preferably 0.08 nm or less, more preferably 0.07 nm or less.

This is because the main plane of the glass substrate as a whole becomes smoother by reducing the average value of the surface roughness Ra.

When the main plane of the glass substrate is smooth as a whole, coarsening of crystal grains can be suppressed when the magnetic layer is formed, and the size of the crystal grains can be reduced and uniform, so that a magnetic film with a uniform and smooth surface can be obtained.

By making the size of the crystal grains small and uniform, the size of the memory spot can be reduced, and the areal recording density of the magnetic recording medium can be improved. Furthermore, the distance between the magnetic disk and the magnetic head can be reduced, and the variation of the distance between the magnetic disk and the magnetic head can be reduced, the occurrence of magnetic noise can be suppressed, and the read/write accuracy and recording density of recording can be improved more than before.

Here, the manufacturing method of the glass substrate for magnetic recording media of this invention is demonstrated.

The glass substrate for magnetic recording media can be manufactured by the manufacturing method including the following process 1-4.

(Step 1) A shape-imparting step of chamfering the inner peripheral end surface and the outer peripheral end surface after processing the original glass substrate into a disk-shaped glass substrate having a hole in the center.

(Process 2) An end surface grinding process of grinding the end surfaces (inner peripheral end surface and outer peripheral end surface) of the glass substrate.

(Step 3) A main plane polishing step of grinding the main plane of the glass substrate.

(Step 4) A cleaning step of finely cleaning and drying the glass substrate.

Then, the glass substrate for magnetic recording media obtained by the manufacturing method including each of the steps described above can be used as a magnetic recording medium by further performing a step of forming a thin film such as a magnetic layer thereon.

Here, in the shape-imparting step of (Step 1), the original glass substrate formed by the float method, the melting method, the press molding method, the down-draw method, or the redraw method is processed into a disc-shaped glass having a round hole in the center. substrate. The original glass substrate used may be amorphous glass, crystallized glass, or strengthened glass having a compressive stress layer (strengthening layer) on the surface of the glass substrate.

Then, in the end surface grinding process of (process 2), end surface grinding|polishing is performed on the end surface (side surface part and chamfer part) of a glass substrate.

In the main plane polishing step of (Step 3), the upper and lower main planes of the glass substrate are simultaneously ground while supplying a polishing liquid to the main planes of the glass substrate using a double-sided polishing apparatus. The polishing of the glass substrate of the present invention may be performed only once, may be performed once and twice, or may be performed three times after the second grinding.

In addition, it is preferable to use a polishing pad previously washed with pure water for 10 minutes or longer as the polishing pad used in the polishing step. This is to suppress aggregation of abrasive grains contained in the polishing liquid.

It should be noted that, as the polishing liquid used in the polishing (finish polishing) carried out at the end of the main surface polishing step, it is preferable to use colloidal silica having a primary particle diameter of 5 nm or more as abrasive grains and having a pH of 3 or more. Slurry.

This is because colloidal silica contained in the polishing liquid has a primary particle size smaller than 5 nm and is likely to aggregate, resulting in problems such as inability to perform stable polishing and an increase in the surface roughness Ra of the main surface.

The primary particle diameter of colloidal silica is preferably 5 nm or more, more preferably 8 nm or more, particularly preferably 10 nm or more. Furthermore, the primary particle diameter of colloidal silica is preferably 30 nm or less, more preferably 28 nm or less, particularly preferably 18 nm or less.

In addition, when the pH of the polishing liquid is less than 3, the value of the surface roughness Ra of the main plane of the glass substrate polished due to the influence of acid may increase. Therefore, the pH of the polishing liquid is preferably 3 or higher, more preferably 3.5 or higher, and particularly preferably 4 or higher.

Before the above-mentioned (step 3) main surface polishing step, lapping (lapping) of the main surface (for example, free abrasive lapping, fixed abrasive lapping, etc.) may be performed. Furthermore, cleaning of the glass substrate (cleaning between processes) and etching of the surface of the glass substrate (etching between processes) may be performed between each process. It should be noted that the grinding of the main plane refers to the grinding of the main plane in a broad sense.

In addition, when high mechanical strength is required for the glass substrate for magnetic recording media, the strengthening process (for example, chemical strengthening process) to form a compressive stress layer (strengthening layer) on the surface layer of the glass substrate may be performed before or after the grinding process. , or between grinding processes.

[Second Embodiment]

In this embodiment, the magnetic recording medium (magnetic disk) using the glass substrate for magnetic recording media demonstrated in 1st Embodiment is demonstrated.

As long as the magnetic recording medium of the present invention uses the glass substrate for magnetic recording medium described in the first embodiment, its structure is not limited, for example, a magnetic layer is provided on the surface of the glass substrate for magnetic recording medium, a protective layer, lubricating layer structure.

The magnetic recording medium has a horizontal magnetic recording method and a perpendicular magnetic recording method, but here the vertical magnetic recording method is taken as an example, and a specific manufacturing method will be described below.

The magnetic recording medium has a magnetic layer, a protective layer, and a lubricating layer at least on its surface. In addition, in the case of a perpendicular magnetic recording method, a soft magnetic underlayer made of a soft magnetic material that functions to circulate a recording magnetic field from a magnetic head is generally arranged. Therefore, for example, a soft magnetic underlayer, a nonmagnetic intermediate layer, a magnetic layer for perpendicular recording, a protective layer, and a lubricating film are laminated in this order from the main plane of the glass substrate.

Each layer will be described below.

As the soft magnetic underlayer, for example, CoNiFe, FeCoB, CoCuFe, NiFe, FeAlSi, FeTaN, FeN, FeTaC, CoFeB, CoZrN, etc. can be used.

Also, the nonmagnetic intermediate layer is made of Ru, Ru alloy, or the like. The non-magnetic intermediate layer has a function of facilitating the epitaxial growth of the magnetic layer for perpendicular recording and a function of breaking the magnetic exchange coupling between the soft magnetic underlayer and the magnetic layer for recording.

The magnetic layer for perpendicular recording is a magnetic film whose magnetization easy axis is oriented in a vertical direction perpendicular to the substrate surface, and contains at least Co and Pt. In addition, in order to reduce interparticle exchange bonding that causes high intrinsic medium noise, a well-segregated fine particle structure (grain structure) is preferable. Specifically, a structure in which oxides (SiO ₂ , SiO, Cr ₂ O ₃ , CoO, Ta ₂ O ₃ , TiO ₂ , etc.), Cr, B, Cu, Ta, Zr, etc. are added to a CoPt-based alloy or the like is used.

The soft magnetic underlayer, nonmagnetic intermediate layer, and magnetic layer for perpendicular recording described so far can be continuously produced by an in-line sputtering method, a DC magnetron sputtering method, or the like.

Next, the protective layer prevents corrosion of the magnetic layer for perpendicular recording and is provided to prevent damage to the surface of the medium even when the magnetic head comes into contact with the medium, and is provided on the magnetic layer for perpendicular recording. As the protective layer, a material containing C, ZrO ₂ , SiO ₂ or the like can be used.

As its formation method, for example, an in-line sputtering method, a CVD method, a spin coating method, or the like can be used.

A lubricating layer is formed on the surface of the protective layer to reduce the friction between the magnetic head and the recording medium (disk). For the lubricating layer, perfluoropolyether, fluorinated alcohol, fluorinated carboxylic acid, etc. can be used, for example. As for the lubricating layer, it can be formed by a dipping method, a spraying method, or the like.

In the magnetic recording medium (magnetic disk) produced by using the glass substrate for magnetic recording medium of the present invention through the procedure described above, since the surface roughness Ra of the main plane of the glass substrate as a whole is within a predetermined range, the magnetic layer formed in the film Coarsening of crystal grains can be suppressed, and the size of crystal grains can be made small and uniform. Thereby, the dot size of the magnetic recording medium can be reduced, and the areal recording density of the magnetic recording medium can be increased. Moreover, since the distance between the magnetic recording medium and the magnetic head can be reduced compared to the past, and the variation of the distance between the magnetic recording medium and the magnetic head can be reduced, the generation of magnetic noise can be suppressed, and the recording efficiency can be improved compared with the past. Read and write accuracy, recording density.

【Example】

Hereinafter, specific examples are given and described, but the present invention is not limited to these examples.

First, methods for evaluating glass substrates for magnetic recording media in the following Examples and Comparative Examples, and methods for evaluating magnetic recording media in which thin films such as magnetic layers are formed on the surface of glass substrates will be described.

(1) Surface roughness (arithmetic mean roughness) Ra

The surface roughness Ra was measured using a scanning interference microscope (manufactured by Zygo, ZeMapper). The measurement area of the surface roughness Ra is a range including the entire recording/reproducing area of the glass substrate for magnetic recording media.

In this example, evaluation areas in the shape of a square grid with a side of 30 μm were set on the entire surface of one main plane of the glass substrate for magnetic recording media, and the surface roughness Ra was obtained for each evaluation area.

(2) Proof test

The proof test evaluates defects (signal quality) of the magnetic layer and the like of the magnetic recording medium. The magnetic head for certification test uses the test head installed on the head slider to reproduce the relationship between the magnetic head and the magnetic disk of the magnetic disk device, and writes, reproduces, erases, and regenerates the write signal for each track of the disk. commented. In this example, EP (Extra Pulse: pulse-eating) errors were evaluated.

The EP error refers to the generation of a reproduced signal that deviates greatly from the amplitude of the reproduced signal of the test head when there is a flaw, foreign matter, poor roughness, or a non-uniform crystal grain size region on the magnetic recording medium. EP errors do not allow proper signal processing of the disk.

In this example, 1000 magnetic recording media were evaluated, and the ratio of the magnetic recording media in which EP errors occurred was defined as the EP occurrence rate.

In the following examples 1 to 10, a glass substrate for a magnetic recording medium and an example in which a magnetic layer and the like are formed on the glass substrate for a magnetic recording medium and used as a magnetic recording medium will be described. Here, Examples 1 to 7 are examples satisfying the requirements of the present invention, and Examples 8 to 10 are comparative examples.

The glass substrates for magnetic recording media of Examples 1 to 10 described below were produced by the following procedure.

In order to obtain a glass substrate for magnetic recording media with an outer diameter of 65 mm, an inner diameter of 20 mm, and a thickness of 0.635 mm, a glass substrate mainly composed of SiO ₂ formed by a float process is processed into a disk-shaped glass substrate with a hole in the center .

In order to obtain a glass substrate for magnetic recording media with a chamfering width of 0.15mm and a chamfering angle of 45°, the inner and outer peripheral end faces of the disk-shaped glass substrate were chamfered (inner peripheral chamfering process, outer peripheral chamfering process) process).

After the chamfering process, the upper and lower main planes of the glass substrate are ground with alumina abrasive grains, and the abrasive grains are cleaned and removed.

Next, use a polishing brush and a polishing liquid containing cerium oxide abrasive grains to polish the outer peripheral side surface and outer peripheral chamfer of the glass substrate for magnetic recording media, and remove the process-induced deterioration layer (scars, etc.) on the outer peripheral side surface and outer peripheral chamfer , Grinding the outer peripheral end face into a mirror surface (peripheral end face grinding process).

After the outer peripheral end face is ground, use a polishing brush and a polishing liquid containing cerium oxide abrasive grains to grind the inner peripheral side and inner peripheral chamfer of the glass substrate for magnetic recording media, and the inner peripheral side and inner peripheral chamfer The process-altered layer (scratch, etc.) is removed, and the inner peripheral end surface is ground to a mirror surface (inner peripheral end surface grinding process). Abrasive grains were cleaned and removed from the glass substrate after the inner peripheral end surface was ground.

After the end face of the glass substrate is processed, the upper and lower main planes of the glass substrate are polished and cleaned using a fixed grain tool containing diamond abrasive grains and a grinding fluid.

Then, as a polishing tool, use a polishing pad made of hard polyurethane and a polishing liquid containing cerium oxide abrasive grains (average particle diameter, hereinafter, referred to as the average particle diameter, and a polishing liquid composition containing cerium oxide of about 1.3 μm), The glass substrate was polished once with a 22B type double-side polishing device (manufactured by SpeedFam, product name: DSM22B-6PV-4MH) so that the polishing amount becomes 20 μm on the upper and lower main planes, and the cerium oxide was cleaned and removed. In addition, 216 glass substrates were polished simultaneously in one batch.

The glass substrate after the primary polishing uses a polishing pad made of soft polyurethane and a polishing liquid containing cerium oxide abrasive grains with an average particle diameter smaller than the above-mentioned cerium oxide abrasive grains (a polishing liquid containing cerium oxide with an average particle diameter of about Composition) as a polishing tool, the upper and lower main planes were polished twice with a 22B type double-sided polishing apparatus so that the polishing amount became 5 μm, and the cerium oxide was cleaned and removed.

The glass substrate polished twice was polished three times (finish polishing). The upper and lower main planes were polished with a double-sided polishing device using a soft polyurethane polishing pad and a polishing liquid containing colloidal silica as a polishing tool for three times of polishing. The above-mentioned soft polyurethane polishing pad was pasted on the polishing table, then subjected to dressing treatment, and washed with pure water for a predetermined period of time in some cases.

In addition, the double-sided polishing apparatus was configured to be able to supply and discharge the polishing liquid, and the polishing liquid was polished while adjusting the supply flow rate of the polishing liquid so that the supply flow rate of the polishing liquid became a predetermined value.

Regarding the cleaning time of the polishing pad, the primary particle size of colloidal silica, the pH of the polishing liquid, the cohesiveness of the colloidal silica contained in the polishing liquid, and the flow rate of the polishing liquid when performing three times of polishing, in the following example It is recorded in 1~10.

Using a particle size distribution measuring device (manufactured by Otsuka Electronics Co., Ltd.: FPAR-1000), the particle size distribution of the polishing liquid before polishing the glass substrate and the particle size distribution of the polishing liquid after polishing the glass substrate are measured, and the d50 value is obtained from the respective particle size distributions , the amount of change (difference) in the d50 value before and after polishing of the glass substrate was calculated to evaluate the cohesiveness of the colloidal silica contained in the polishing liquid.

In addition, the above-mentioned d50 value means the particle diameter at which the integrated value becomes 50% when the number conversion is carried out from the scattering intensity distribution.

Specifically, evaluation was performed by the amount of change in the d50 value before and after polishing calculated by the following formula. It is represented by [d50 value (nm) of the polishing liquid after polishing]-[d50 value (nm) of the polishing liquid before polishing].

When the change in the d50 value before and after polishing calculated by the above formula is 15nm or less, the aggregation of the abrasive grains (colloidal silica) contained in the polishing liquid hardly occurs and the dispersibility is good (A). Agglutination occurs (B). Moreover, when it is 31 nm or more, the aggregation (C) of the grade which affects the polishing of the main plane of a glass substrate arises.

In order to obtain a glass substrate for a magnetic recording medium that satisfies the requirements of the present invention, it is preferable to use a polishing liquid (A) that hardly aggregates abrasive grains contained in the polishing liquid and has good dispersibility. This is because when using a polishing liquid in which abrasive grains tend to agglomerate, a portion with locally high surface roughness Ra may occur on the surface of the glass substrate for magnetic recording media, and the glass substrate that has been finely ground (three times) is sequentially Scrubbing, ultrasonic cleaning in a state of immersion in a detergent solution, ultrasonic cleaning in a state of immersion in pure water (precision cleaning), and drying with isopropanol vapor were performed.

Surface roughness Ra was evaluated by the method mentioned above about the whole surface of the main plane of the glass substrate for magnetic recording media obtained by the above procedure.

Moreover, on the surface of the glass substrate for magnetic recording media obtained by the above procedure, the multilayer film which has a magnetic layer was formed into a film by the following procedure as a magnetic recording medium, and EP occurrence rate was evaluated.

On the surface of the glass substrate for magnetic recording media that has been cleaned before film formation, an NiFe layer as a soft magnetic base layer, a Ru layer as a nonmagnetic intermediate layer, and a Ru layer as a perpendicular magnetic recording layer are sequentially laminated using an in-line sputtering device. Granular structure layer of _CoCrPtSiO2 . Next, a diamond-like carbon film is formed as a protective layer by a CVD method. Then, a lubricating film containing perfluoropolyether was formed by a dipping method.

With respect to the obtained magnetic recording medium, EP errors were evaluated by the method described above, and the EP occurrence rate was obtained.

The conditions of the polishing solution for the finish polishing (three times polishing) of the main plane are described in the following Examples 1 to 10. Example 1～Example 7 are embodiments, and Example 8～Example 10 are comparative examples.

Surface roughness Ra maximum value/surface roughness Ra average value, surface roughness Ra average value (nm) on the entire surface of the main plane of the glass substrate for magnetic recording media processed under the processing conditions of Examples 1 to 10 , Surface roughness Ra standard deviation (nm) as shown in Table 1. Furthermore, Table 1 also shows the EP occurrence rate (%) of the magnetic recording medium.

(example 1)

For the glass substrate for magnetic recording media that has been subjected to the processing up to the second grinding of the main plane grinding by the above-mentioned procedure, the finish grinding of the main plane grinding was carried out (three grinding steps).

The finish polishing was performed using a soft polyurethane polishing pad previously washed with pure water for 10 minutes, and a polishing solution of pH 4 containing colloidal silica with a primary particle diameter of 12 nm as abrasive grains. When the cohesiveness of the abrasive grains (colloidal silica) contained in the polishing liquid was evaluated, the amount of change in the d50 value of the polishing liquid before and after polishing was 15 nm or less, which was good (A).

Moreover, polishing was performed so that the flow rate of the polishing liquid supplied to the polishing surface of a double-sided polishing apparatus might become 6 ml/min per glass substrate for magnetic recording media.

The glass substrate for magnetic recording media was obtained by fine-cleaning the glass substrate after the main plane processing, and the surface roughness Ra of the main plane of the glass substrate for magnetic recording media was measured and evaluated.

In addition, as described above, a multilayer film having a magnetic layer was deposited on the surface of a glass substrate for magnetic recording media to form a magnetic recording medium, and the EP generation rate was evaluated.

(Example 2)

In the finish grinding (three times of grinding process) of the main plane grinding, except that the flow rate of the polishing liquid supplied to the grinding surface of the double-sided grinding device is 2 ml/min for each glass substrate for magnetic recording media, by and Example 1 A glass substrate for a magnetic recording medium and a magnetic recording medium (magnetic disk) were produced in the same manner as in Example 1.

It should be noted that the cohesiveness of the abrasive grains (colloidal silica) contained in the polishing liquid used for finish polishing was good (A) as in the case of Example 1.

Moreover, it evaluated similarly to Example 1 about the obtained glass substrate for magnetic recording media, and a magnetic recording medium. The results are shown in Table 1.

(Example 3)

In the finishing polishing (three polishing steps) of the main surface polishing, except that the pH of the polishing liquid is set to 5, the flow rate of the polishing liquid supplied to the polishing surface of the double-sided polishing device is set to 2 ml per glass substrate for magnetic recording media. Except /min, the glass substrate for magnetic recording media and a magnetic recording medium (magnetic disk) were manufactured by the method similar to Example 1.

In addition, the cohesiveness of the abrasive grains (colloidal silica) contained in the polishing liquid used at the time of finish polishing was good (A) similarly to the case of Example 1.

Moreover, it evaluated similarly to Example 1 about the obtained glass substrate for magnetic recording media, and a magnetic recording medium. The results are shown in Table 1.

(Example 4)

In the finishing polishing (three polishing steps) of the main surface polishing, in addition to using a polishing liquid with a primary particle diameter of 20 nm of colloidal silicon oxide contained in the polishing liquid, the polishing liquid supplied to the polishing surface of the double-sided polishing device is provided. The glass substrate for magnetic recording media and the magnetic recording medium (magnetic disk) were manufactured by the method similar to Example 1 except that the flow rate of liquid was 2 ml/min per glass substrate for magnetic recording media.

In addition, the cohesiveness of the abrasive grains (colloidal silica) contained in the polishing liquid used at the time of finish polishing was good (A) similarly to the case of Example 1.

Moreover, it evaluated similarly to Example 1 about the obtained glass substrate for magnetic recording media, and a magnetic recording medium. The results are shown in Table 1.

(Example 5)

In the finishing polishing (three polishing steps) of the main surface polishing, in addition to using a polishing liquid with a primary particle diameter of 25 nm of colloidal silicon oxide contained in the polishing liquid, the polishing liquid supplied to the polishing surface of the double-sided polishing device is provided. The glass substrate for magnetic recording media and the magnetic recording medium (magnetic disk) were manufactured by the method similar to Example 1 except that the flow rate of liquid was 2 ml/min per glass substrate for magnetic recording media.

In addition, the cohesiveness of the abrasive grains (colloidal silica) contained in the polishing liquid used at the time of finish polishing was good (A) similarly to the case of Example 1.

Moreover, it evaluated similarly to Example 1 about the obtained glass substrate for magnetic recording media, and a magnetic recording medium. The results are shown in Table 1.

(Example 6)

In the finishing polishing (three polishing steps) of the main surface polishing, the primary particle diameter of the colloidal silica contained in the polishing liquid is set to 30nm, and the flow rate of the polishing liquid supplied to the polishing surface of the double-side polishing device is set A glass substrate for a magnetic recording medium and a magnetic recording medium (magnetic disk) were produced by the same method as in Example 1 except that the glass substrate for a magnetic recording medium was 2 ml/min.

In addition, the cohesiveness of the abrasive grains (colloidal silica) contained in the polishing liquid used at the time of finish polishing was good (A) similarly to the case of Example 1.

Moreover, it evaluated similarly to Example 1 about the obtained glass substrate for magnetic recording media, and a magnetic recording medium. The results are shown in Table 1.

(Example 7)

In the finish grinding (3 grinding steps) of the main plane grinding, except making the grinding liquid pH3, and the flow rate of the grinding liquid supplied to the grinding surface of the double-sided grinding device is 2 for each glass substrate for magnetic recording media. A glass substrate for a magnetic recording medium and a magnetic recording medium (magnetic disk) were produced by the same method as in Example 1 except for milliliters/minute.

In addition, the cohesiveness of the abrasive grains (colloidal silica) contained in the polishing liquid used at the time of finish polishing was good (A) similarly to the case of Example 1.

Moreover, it evaluated similarly to Example 1 about the obtained glass substrate for magnetic recording media, and a magnetic recording medium. The results are shown in Table 1.

(Example 8)

In the finishing polishing (three polishing steps) of the main plane polishing, except using a polishing pad that is not cleaned with pure water, and setting the flow rate of the polishing liquid supplied to the polishing surface of the double-sided polishing device for each magnetic recording The glass substrate for magnetic recording media and the magnetic recording medium (magnetic disk) were manufactured by the same method as Example 1 except that the glass substrate for media was 2 ml/min.

In addition, regarding the cohesiveness of the abrasive grains (colloidal silica) contained in the polishing liquid used for finishing polishing, the particle size distribution d50 of the polishing liquid changes by 31 nm or more before and after polishing, which is (C) .

Moreover, it evaluated similarly to Example 1 about the obtained glass substrate for magnetic recording media, and a magnetic recording medium. The results are shown in Table 1.

(Example 9)

In the finishing grinding (three times of grinding process) of the main surface grinding, except that the cleaning time of the polishing pad based on pure water is 5 minutes, and the flow rate of the polishing liquid supplied to the polishing surface of the double-sided polishing device is set to be 5 minutes for each The glass substrate for magnetic recording media and the magnetic recording medium (magnetic disk) were manufactured by the method similar to Example 1 except that the glass substrate for magnetic recording media was 2 ml/min.

It should be noted that regarding the cohesiveness of the abrasive grains (colloidal silica) contained in the polishing liquid used at the time of finish polishing, the amount of change in the d50 value of the polishing liquid before and after polishing is 16 nm or more and 30 nm or less, for (B).

Moreover, it evaluated similarly to Example 1 about the obtained glass substrate for magnetic recording media, and a magnetic recording medium. The results are shown in Table 1.

(Example 10)

In the fine grinding (3 times of grinding process) of main surface grinding, except that the polishing liquid is pH2, and the flow rate of the polishing liquid is 2 milliliters per minute for each glass substrate for magnetic recording media, the same as in example 1 A glass substrate for a magnetic recording medium and a magnetic recording medium (magnetic disk) were produced by the method.

It should be noted that, regarding the cohesiveness of the abrasive grains (colloidal silica) contained in the polishing liquid used at the time of finish polishing, before and after polishing, the change in the d50 value of the polishing liquid is 15 nm or less, which is good ( A).

Moreover, it evaluated similarly to Example 1 about the obtained glass substrate for magnetic recording media, and a magnetic recording medium. The results are shown in Table 1.

From the results in Table 1, it can be confirmed that the EP generation rate of the magnetic recording media produced using the glass substrates for magnetic recording media of Examples 1 to 7 satisfying the provisions of the present invention was all reduced to 1.6% or less. On the other hand, it can be seen that the incidence of EP in Examples 8 to 10, which are comparative examples, is as high as about 2.5% at the lowest.

This is considered to be because the glass substrate for magnetic recording media of the present invention does not have a region where the surface roughness Ra is locally high throughout the main plane, and the entire main plane becomes smooth. When , it is possible to suppress the crystal grains from becoming locally enlarged.

Therefore, it is considered that the occurrence of magnetic noise can be suppressed, the accuracy of reading and writing to the magnetic recording medium by the magnetic head can be improved, and a decrease in recording density can be prevented.

【Table 1】

Claims (6)

1. a glass base plate for magnetic recording carrier, has a pair principal plane, it is characterised in that

On at least one principal plane, whole of the principal plane in the record regenerating region when comprising as magnetic recording media sets Fixed area is 25 μm²～2500 μm²The meansigma methods of surface roughness Ra that is measured to of cancellate each evaluation region be Below 0.07nm,

The maximum of described surface roughness Ra is less than 1.4 times of the meansigma methods of described surface roughness Ra.

Glass base plate for magnetic recording carrier the most according to claim 1, wherein,

The grid set on whole of the described principal plane in the record regenerating region when comprising as described magnetic recording media 1.3 times of the meansigma methods that maximum is described surface roughness Ra of the surface roughness Ra that each evaluation region of shape is measured to Below.

Glass base plate for magnetic recording carrier the most according to claim 1 and 2, wherein,

The grid set on whole of the described principal plane in the record regenerating region when comprising as described magnetic recording media The standard deviation of the surface roughness Ra that each evaluation region of shape is measured to is below 0.012nm.

Glass base plate for magnetic recording carrier the most according to claim 1 and 2, wherein,

The grid set on whole of the described principal plane in the record regenerating region when comprising as described magnetic recording media The meansigma methods of the surface roughness Ra that each evaluation region of shape is measured to is below 0.06nm.

Glass base plate for magnetic recording carrier the most according to claim 3, wherein,

The grid set on whole of the described principal plane in the record regenerating region when comprising as described magnetic recording media The meansigma methods of the surface roughness Ra that each evaluation region of shape is measured to is below 0.06nm.

6. a magnetic recording media, it uses the glass base plate for magnetic recording carrier according to any one of Claims 1 to 5.